Advanced structural ceramic materials have gained the attention of industry by virtue of their superior performance qualities. These qualities, such as superior high temperature strength, high toughness, resistance to thermal shock and resistance to oxidation provide the basis for their potential use in a variety of applications.
Despite their enormous potential, advanced structural ceramics in general and silicon nitride in particular have yet to capture many markets, principally due to the perception that they tend toward catastrophic failure, and thus are unsuitable for uses in applications requiring high reliability.
While significant progress has been made in the development of strong, tough, refractory ceramics for demanding applications such as the AGT rotor, processing these materials sometimes still introduces strength-limiting and reliability-reducing flaws.
One measure of the extent of the presence of flaws is the tensile strength of the ceramic. Typically, a conventional ceramic material often possesses a tensile strength in the neighborhood of only between about 50% and 90% of its flexural strength. Accordingly, the average tensile strength of conventional silicon nitride materials is often in the range of about 650 to 750 MPa.
Accordingly, it is the object of the present invention to provide a silicon nitride ceramic having an average tensile strength of at least about 800 MPa.